The Civil Human Rights Front have revieved a letter of objection, stopping them from organising a planned march from Victoria Park to Chater Gardens on Sunday afternoon.
The plan was to leave the Causeway Bay park at 3pm and walk to Central, passing through Wan Chai and Admiralty. Before security measures were increased recently at the Central Government Offices, most protests applied to end there, as it is seen as a more symbolic route.
The Front, which organised two previous million-man marches, had applied for permission for a total of 300,000 participants. They have vowed to appeal.
In a statement, convenor Jimmy Sham Tsz-kit said the Front was "extremely unhappy" with the police decision.
In the letter, the police only grant permission for a gathering in Victoria Park from 10am to 11pm, on grounds of public safety and public order.